Programas para la atención de población en condi ción de vulnerabilidad

The most common c la s s if ic a t io n scheme fo r muscle typ es separates fib r e s on the b a s is o f th e ir con traction v e lo c ity (C lose 1972)* I t i s

w idely accepted th at the speed o f con traction i s co rrela ted w ith the a c tiv ity and pH s t a b ilit y o f the C a^^-activated m y o fib rilla r ATPase (barany I967» Bone 1978; F litn e y & Johnston 1979')* This scheme may be extended to in clud e referen ce to the enzyme and m etab olite p r o file (Nemeth e t a l 1979)» in order to d istin g u ish between m uscles o f a sim ila r speed o f co n tra ctio n , but

d iffe r in g p attern s o f enzyme a c t iv it y (C lose 1972; Bone e t a l 1978; A kster and Osse 1978) .

H eterogeneity in the h is to lo g ic a l appearance o f t e le o s t s k e le ta l muscle has been known fo r some tim e (Creepe, 1913), but th ere has been no attem pt to analyse th e v a r ia tio n in fib r e stru ctu re or d istr ib u tio n o f fib r e ty p es, w ith resp ect to p o sitio n in the myotome. Frevious stu d ies on f is h muscle h istoch em istry and fin e stru ctu re have u su a lly in volved random, or

semi-random, sam pling o f d iffe r e n t m uscle reg io n s. 14any workers extrap olate th e data from sm all sample s iz e s to im ply a homogeneity o f fib r e iype th r o u ^ - out the myotome. In e e l s , the elongate body and a n g u illifo rm mode o f

swimming i s r e fle c te d in a r e la t iv e ly sta b le red:w hite m uscle r a tio along the len gth o f the trunk, in co n tra st to the ^ub-carapgiform locom otion shown by cod, which demands a dramatic in crea se ip the proportion o f red muscle towards the caudal peduncle (se e a lso Mosse and Hudson 1977)* T his i s o f consid erab le advantage fo r reproducible sampling o f tl^e m uscle.

The sm all s iz e o f the e lv e r introduqes d i f f i c u l t i e s in studying the d iffe r e n tia tio n o f m uscle fib r e typ es u sin g biochem ical c r it e r ia alon e. Q u a lita tiv e h isto ch em istry , on the oth er hand, a llow s th e id e n tific a tio n o f enzyme system s w ithout m icro d issectio n apd g iv e s d ir e c tly comparable r e s u lts fo r d iffe r e n t anatom ical region s o f the in ta c t specimen. With such a sm all animal a more d e ta ile d exam ination o f reg io n a l d iffe r e n c e s in fin e stru ctu re,

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fib re typ es, and v a sc u la r isa tio n w ithin the myotome i s p o s sib le , than can be made with la rg er f is h . Such d e ta ile d d escrip tio n i s e s s e n tia l to an understanding o f the developmental p ro cesses (fib r e p r o life r a tio n and d iffe r e n tia tio n ) underlying metamorphosis and post-em bryonic muscle growth in t h is type o f f is h .

There have been few h is to lo g ic a l stu d ies concerning p rim itiv e t e le o s t s , although some q u a lita tiv e and sem i-q u an titativ e data i s a v a ila b le fo r sub­ adult e e ls (Bostrom and Johansson 1972; V/illemse and de R uiter 1979;

Hulbert and Moon 1978a^ S im ila rly , th ere i s l i t t l e inform ation a v a ila b le about the c a p illa r y supply and blood flow to f is h muscle (S teven s, 19&8; Boddeke e t a l 1959)» The r e s u lts in d ic a te a co rr ela tio n between muscle a c t iv it y , as a fu n ction o f aerobic ca p a city , and the development o f the c a p illa r y network (Bone 1978; Mosse 1978). This study provides the f i r s t q u a lita tiv e d escrip tio n o f muscle fib r e type h eterogen eity w ithin the myotome and th e f i r s t q u a n tita tiv e d escrip tio n o f o a p illa r is a tio n , in a t e le o s t

■with fo c a lly innervated f a s t fib r e s .

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O

a t 20 - 1 C fo r s ix months p rio r to sam pling, Freshwater l i f e was